From a mechanical perspective, the cornea of an eye includes a Bowman's membrane that has exceptionally good tensile strength. Anatomically, Bowman's membrane is a relatively thin layer of tissue that is located just under the epithelium on the anterior surface of the cornea. More specifically, Bowman's membrane extends across the cornea, and its peripheral edge connects with the sclera. Most corneal tissue, however, is not in Bowman's membrane. Instead, it is in the stroma, which is tissue that lies immediately under (posterior) Bowman's membrane. In comparison with Bowman's membrane, although the stroma has significantly more tissue, it has substantially less structural strength.
In the eye, behind (posterior) the cornea is the aqueous humor. Aqueous humor is a clear fluid that fills the space between the lens and the cornea. Importantly, the aqueous humor exerts an intraocular pressure (IOP) against the posterior surface of the cornea. Reactive forces against this IOP are provided by both Bowman's membrane and the stroma.
It can happen for any of various reasons that, during the physical development of an eyeball, the anterior surface of the cornea will sometimes be formed with superficial irregularities, such as topographical depressions or bulges. Moreover, these irregularities persist under the influence of biomechanical forces that develop mostly in the stroma. In more detail, the biomechanical forces that naturally result in the stroma, in reaction to IOP, develop stress distribution patterns that maintain the topography of the eye's anterior surface, with or without irregularities. When irregularities are present, however, the consequences are the creation of optical aberrations. As is well known, these aberrations can be corrected (eliminated or minimized) by returning the anterior surface of the cornea to a normal, substantially spherical shape.
In light of the above, it is an object of the present invention to provide a system and method wherein existing biomechanical forces in the stroma are weakened to disrupt their stress distribution patterns, and thereby allow IOP to reshape the eye's anterior surface. Another object of the present invention is to provide a system and method wherein the location of stress distribution patterns in the stroma are determined and targeted for disruption with reference to deviations in the topography of the eye's anterior surface. Still another object of the present invention is to provide a system and method wherein topographical deviations from a reference datum identify tissue volumes under the deviation, and Laser Induced Optical Breakdown (LIOB) is performed on boundary surfaces of the underlying volume to disrupt stress distribution patterns. Yet another object of the present invention is to provide a system and method for altering a configuration of a transparent material (e.g. a cornea) that is easy to use, is simple to implement and is comparatively cost effective.